Apparatus and method for using an LED for backlighting and ambient light sensing

ABSTRACT

Embodiments of a backlight module for illuminating a liquid crystal display (LCD) and sensing ambient light are provided herein. The backlight module includes a light-emitting diode (LED) array and a backlight controller. The backlight controller is configured to forward bias the LED array to backlight the LCD and reverse bias the LED array to sense the ambient light level. The backlight controller is configured to adjust the brightness of the LED array based on the current ambient lighting conditions sensed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/045,038, filed Mar. 10, 2011, which claims the benefit of U.S.Provisional Patent Application No. 61/437,379, filed Jan. 28, 2011, allof which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This application relates generally to backlighting and ambient lightsensing and more particularly to backlighting and ambient light sensingusing a light-emitting diode (LED).

BACKGROUND

Liquid crystal displays (LCDs) are used in a wide range of electronicdevices and appliances, from small handheld mobile phones all the way upto large-panel TVs. In general, three main types of LCDs exist and eachhas characteristics that suit different applications. These three LCDtypes include: transmissive, reflective, and transflective LCDs.Transmissive and transflective LCDs are of particular relevance to thedescription herein and are described further below.

A transmissive LCD provides high brightness, contrast, and colorsaturation and is characterized by its use of a backlight (i.e., aninternal light source positioned at the back of the LCD) to provideillumination. The backlight in a transmissive display is typicallyconstructed from white light-emitting diodes (LEDs). The powerconsumption associated with these backlight LEDs can be relatively highbecause they are often driven with sufficient power to provide enoughlight output to compete with the strongest ambient light environmentsthat a device may be operated within, such as outdoor environments wheresunlight can be strong.

One solution used to combat the issue of high power consumption is theinclusion and positioning of an ambient light sensor on the outersurface of the LCD. The ambient light sensor is used to estimate theambient light conditions of the environment where the LCD is currentlyoperating, which is then used to adjust the brightness of the backlightLEDs to meet, but not greatly exceed, the brightness required for theambient light conditions. Although this solution can improve powerconsumption, the addition of an ambient light sensor adds cost to thedisplay and increases its overall size. In addition, conventionalimplementations of transmissive displays that utilize ambient lightsensors do not take into consideration the amount of light that thedisplay's own screen adds to the estimated ambient light conditionssensed. Therefore, the brightness of the screen is often adjusted to asub-optimal setting.

A transflective LCD combines both transmissive functions and reflectivefunctions into one display. In dark or low ambient level conditions, thebacklight is turned on and the image is primarily displayed in thetransmissive mode. In bright ambient light situations, such as understrong sunlight, the reflective mode primarily functions to illuminatethe LCD and the backlight may either be turned on to aid the display ofan image or turned off to save power. In the reflective mode, the LCD isspecifically illuminated by an external light source, which passesthrough the front of the LCD and is reflected back by an embeddedreflector in the back of the LCD. Because a transflective LCD operatingin the reflective mode relies on external light to display an image, ithas low power consumption and good readability in high ambient lightenvironments.

To estimate current ambient light conditions such that, in brighterenvironments, the brightness of the backlight can be reduced to allowthe reflective mode of a transflective display to take over, an ambientlight sensor is typically used. Although this solution can improve powerconsumption, the addition of an ambient light sensor, as noted above,adds cost to and increases the overall size of the display.

Therefore, what is needed is an apparatus and method for estimatingambient light conditions for an LCD, while at the same time eliminatingthe need for a traditional ambient light sensor and the drawbacksassociated therewith.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 illustrates an exploded view of an exemplary LCD.

FIG. 2 illustrates a partial block diagram of an LCD that uses atraditional ambient light sensor.

FIG. 3 illustrates a block diagram of an LCD that uses a backlightambient light sensor, according to embodiments of the present invention.

FIG. 4 illustrates an exemplary backlight module, according toembodiments of the present invention.

FIG. 5 illustrates an exemplary method for adjusting the brightness ofan LCD based on ambient light conditions sensed by a backlight ambientlight sensor, according to embodiments of the present invention.

The present invention will be described with reference to theaccompanying drawings. The drawing in which an element first appears istypically indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the invention. However, itwill be apparent to those skilled in the art that the invention,including structures, systems, and methods, may be practiced withoutthese specific details. The description and representation herein arethe common means used by those experienced or skilled in the art to mosteffectively convey the substance of their work to others skilled in theart. In other instances, well-known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the invention.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

1. Example Operating Environment

FIG. 1 illustrates an exploded view of an exemplary transmissive ortransflective LCD 100 in which embodiments of the present invention canbe implemented. LCD 100 specifically includes a backlight module 110, afirst polarizing film 120, a liquid crystal sandwich 130, and a secondpolarizing film 140. LCD 100 can be used within several differentdevices, including a mobile phone, video camera, television, or monitor,to name a few.

In operation, liquid crystal sandwich 130 is controlled by a graphicscontroller (not shown) to allow varying, amounts of light from backlightmodule 110 to pass through different portions of second polarizing film140. By controlling the amount of light that passes through portions ofsecond polarizing film 140, a desired image can be produced by LCD 100as will be explained further below.

In order to produce light that can be filtered by liquid crystalsandwich 130, backlight module 110 includes an array of LEDs (not shown)that can be positioned along one or more edges of a back panel of LCD100 or dispersed over the area of a back panel of LCD 100. The lightproduced by backlight module 110 initially passes through firstpolarizing film 120 that is configured to convert the light into lightwith a single polarization. For example, first polarizing film 120 canbe a wire-grid polarizer that is configured to transmit horizontalcomponents of the light passing through it while absorbing and/orreflecting vertical components. In general, polarizing film 120 can beconfigured to transmit any single polarization angle.

The polarized light from first polarizing film 120 is subsequentlyprocessed by liquid crystal sandwich 130, which has been broken down onthe right side of FIG. 1 to further illustrate and describe itsconstituent components. In particular, liquid crystal sandwich 130includes (starting from the components closest to the back of LCD 100) afirst glass plate 150, a back electrode 155, a first polymer layer 160,a front electrode/second polymer layer 165, an RGB mask 170, and asecond glass plate 175.

Between the first polymer layer 160 and second polymer layer 165 areliquid crystals (e.g., nematic liquid crystals) that exhibit certainoptical properties that can be controlled by an applied electric field.More specifically, and in one embodiment, twisted configurations (e.g.,helical structures) of liquid crystal molecules are formed between thetwo polymer layers, which are separated by a series of spacers (notshown). Each polymer layer has “grooves” on its surface that areoriented at 90 degrees relative to one another such that the two ends ofeach configuration of liquid crystal molecules align to the grooves,twisting each configuration by 90 degrees when no external electricfield is applied. The twist of each configuration of liquid crystalmolecules reorients or bends the light that has passed through firstpolarizing film 120 and glass plate 150 by 90 degrees, allowing it toeventually pass through glass plate 175 and second polarizing film 140,which is oriented 90 degrees out of phase with first polarizing film120.

By applying an external electric field across the layer of liquidcrystals between polymer layers 160 and 165, each twisted configurationof liquid crystal molecules can be untwisted and aligned parallel to theelectric field. Adjusting the intensity of the applied electrical fieldallows the amount of untwisting, to be controlled and, thereby, theamount of light that is able to eventually pass through secondpolarizing film 140.

Back electrode 155 and front electrode 165 are specifically used togenerate and apply an electric field across the layer of liquidcrystals. For example, and in one embodiment, the display area of LCD100 is divided into a two-dimensional array of pixels, which are eachfurther divided into three areas. Back electrode 155 and front electrode165 are configured to generate and apply a uniquely controlled electricfield across each portion of the layer of liquid crystals correspondingto the three areas of each pixel. The light passing through the threeareas of each pixel is subsequently processed by RGB mask 170, whichrespectively filters the light passing through the three areas of eachpixel with a red, green, and blue color filter. Thus, back electrode 155and front electrode 165 can be controlled to adjust the amount of red,green, and blue light that makes up each blended pixel color displayedby LCD 100 and, consequently, the ultimate image displayed.

In one embodiment, an active matrix scheme is implemented by LCD 100 togenerate and apply different electric fields across different portionsof the layer of liquid crystals. In another embodiment, a passive matrixscheme is used.

It should be noted that the graphics controller for controlling backelectrode 155 and front electrode 165 is not shown in FIG. 1. It shouldbe further noted that LCD 100 represents only one exemplary LCD in whichembodiments of the present invention can be implemented. For example,and as would be appreciated by one of ordinary skill in the art,embodiments of the present invention can be implemented in anyreasonable transmissive or transflective LCD that uses an array of LEDsto provide backlight illumination.

2. Conventional Ambient Light Sensor

Often the power consumption associated with LEDs in the backlight of anLCD, such as LCD 100, can be relatively high because the LEDs are oftendriven with sufficient power to provide enough light output to competewith the strongest ambient light environments a device may be operatedwithin, such as outdoor environments where sunlight can be strong.

One solution used to combat the issue of high power consumption is theinclusion and positioning of an ambient light sensor on the surface ofan LCD. The ambient light sensor is used to estimate the ambient lightconditions of the environment where the LCD is currently operating,which is then used to adjust the brightness of the backlight LEDs tomeet, but not greatly exceed, the brightness required for the ambientlight conditions.

FIG. 2 illustrates a block diagram of an exemplary control structure200, for controlling LCD 100, that uses a traditional ambient lightsensor 285 as described above. Control structure 200 specificallyincludes a graphics controller 210 for controlling back electrode 155via gate driver 220 and source driver 225, and a backlight controller230 for controlling LED array 240 containing LEDs that provide light 250that passes through back electrode 155.

In one embodiment, back electrode 155 is configured to be operated in anactive matrix scheme and includes an array of pixel elements 260 thateach correspond to one color (i.e., red, green, or blue) of a completepixel. Each pixel element specifically includes a transistor and acapacitor (one end of this capacitor is disposed on front electrode 165illustrated in FIG. 1). This transistor/capacitor pair is often referredto as a thin film transistor (TFT).

Gate driver 220 uses a series of scan lines 270 to drive the gates ofthe transistors of each pixel element 260, thereby turning, thetransistors on and off. Source driver 225 uses a series of data lines280 to drive either the source or drain of the transistors of each pixelelement 260 to charge each associated capacitor when the transistor ison. Graphics controller 210 is configured to control gate driver 220 andsource driver 225 to turn on and off select ones of pixel elements 260and to charge each capacitor of pixel elements 260 to a desired voltagelevel. The voltage across each capacitor induces a proportional electricfield across the corresponding area of the liquid crystal layer, whichin turn changes the orientation or twist of the configurations of liquidcrystal molecules within that area. As discussed above, the amount oftwist of the liquid crystal configurations effects the amount of light250 that is eventually passed through to the output display of LCD 100.Thus, by appropriately controlling the amount of charge stored on eachcapacitor of pixel elements 260, graphics controller 210 can format theoutput display of LCD 100 to display a desired image.

It should be noted that the active matrix scheme discussed aboverepresents only one potential scheme for controlling the orientation ofthe liquid crystals associated with each pixel element 260. Otherpossible control schemes are possible without departing from the scopeand spirit of the present invention as would be appreciated by one ofordinary skill in the art. For example, and in another embodiment, apassive matrix scheme can be used.

Backlight controller 230 is further included in control structure 200and is configured to supply power to LED) array 240 and control thebrightness of LED array 240 using a pulse width modulation (PWM) dimmingtechnique. Using the PWM dimming technique, backlight controller 230modulates the time that the LEDs in LED array 240 are on using a PWMdrive signal 295. The brightness of the LCD roughly equates to the dutycycle of PWM drive signal 295.

The ability to control brightness is coupled with traditional ambientlight sensor 285 so that the brightness of LED array 240 can be adjustedbased on the current lighting conditions of the environment where thedevice is being used. For example, in a room where the sensed ambientlight level 290 is fairly bright, backlight controller 230 can adjustthe duty cycle of PWM drive signal 295 to provide a high brightnesslevel. However, in a room where the ambient light level 290 is fairlydim, backlight controller 230 can adjust the duty cycle of PWM drivesignal 295 to provide a low brightness level.

Although the ability to control brightness for sensed ambient lightconditions can improve power consumption, the addition of traditionalambient light sensor 285 adds cost to the display and increases itsoverall size. In addition, many implementations of displays that utilizeambient light sensors, such as ambient light sensor 285, do not takeinto consideration the amount of light that the display's own screenadds to the estimated ambient light conditions sensed. Therefore, thebrightness of the screen is often adjusted to a sub-optimal setting.

Embodiments of the present invention, discussed further below, aredirected to apparatuses and methods for estimating ambient lightconditions for an LCD, while at the same time eliminating the need for atraditional ambient light sensor, such as ambient light sensor 285, andthe drawbacks associated therewith.

3. Backlight Ambient Light Sensor

FIG. 3 illustrates a block diagram of an exemplary control structure 300for controlling LCD 100, according to embodiments of the presentinvention. Control structure 300 specifically includes substantiallysimilar components as control structure 200 illustrated in FIG. 2.However, traditional ambient light sensor 285 has been eliminated andreplaced by a backlight ambient light sensor (BALS) (not shown). Inaddition, backlight controller 230 illustrated in FIG. 2 has beenfurther replaced by a modified backlight controller 310.

In operation, backlight controller 310 is configured to supply power toLED array 240 and control the brightness of LED array 240 using a pulsewidth modulation (PWM) dimming technique. Using the PWM dimmingtechnique, backlight controller 310 modulates the time that the LEDs inLED array 240 are on using PWM drive signal 295. The brightness of theLCD roughly equates to the duty cycle of PWM drive signal 295.

In an embodiment, one or more of the LEDs used to perform backlightingin LED) array 240 are further used as ambient light sensors by backlightcontroller 310, thereby functioning as a BALS. By reusing one or more ofthe LEDs to perform the extra functionality of ambient light sensing,the traditional ambient light sensor can be eliminated. In order for theLEDs to perform the dual-functionality mentioned above, the LEDs areforward biased to produce light and reverse biased to perform ambientlight sensing by backlight controller 310.

In a further embodiment of the present invention, the one or moredual-functioning LEDs of LED array 240 are reverse biased and functionas ambient light sensors during the phase of PWM drive signal 295 thattraditionally turns the LEDs off. In a variant of this embodiment, theone or more dual-functioning LEDs are reverse biased and function asambient light sensors only during select cycles of PWM drive signal 295;i.e., during some but not every cycle of PWM drive signal 295. Forexample, the one or more dual-functioning LEDs are reverse biased andfunction as ambient light sensors for one in every N cycles of PWM drivesignal 295, where N is an integer number. In another example, the one ormore dual-functioning LEDs are reverse biased and function as ambientlight sensors for M cycles in every N cycles of PWM drive signal 295,where M and N are integer numbers and M is less than N.

The brightness of LED array 240 can subsequently be adjusted based onthe current lighting conditions sensed by the one or more LEDs in LEDarray 240. For example, in a room where the sensed ambient light level320 is fairly bright, backlight controller 310 can adjust the duty cycleof PWM drive signal 295 to provide a high brightness level. However, ina room where the sensed ambient light level 320 is fairly dim, backlightcontroller 310 can adjust the duty cycle of PWM drive signal 295 toprovide a low brightness level.

In another embodiment of the present invention, additional control logiccan be further utilized by backlight controller 310 to receive and useinformation regarding the state of the crystalline material of LCD 100to interpret and/or adjust the ambient light level sensed by the one ormore dual-functioning LEDs. More specifically, the current orientationor twist of the configurations of liquid crystal molecules correspondingto one or more pixel elements 260 of LCD 100 at the time the ambientlight level is sensed by the one or more dual-functioning LEDs can beused to interpret and/or adjust the sensed ambient light level 320.

For example, if the current orientation or twist of the configurationsof liquid crystal molecules is such that less light is allowed to passthrough the LCD display than what would otherwise be possible, then theambient light level sensed can be inflated and/or interpreted tocorrespond to an actual ambient light level having a brightness greaterthan what was actually sensed. This information regarding the state ofthe crystalline material of LCD 100 can be in the form of the voltageacross the capacitor corresponding to one or more pixel elements 260, orthe amount of charge stored thereon, and can be received by backlightcontroller 310 from graphics controller 210 via graphics coordinationsignal 330, as illustrated in FIG. 3.

In another embodiment, additional control logic can be further utilizedby backlight controller 310 to receive and use information regarding thebrightness of a number of pixel elements 260 of LCD 100 to interpretand/or adjust the ambient light level sensed by the one or moredual-functioning LEDs. For example, the brightness, or him, of a pixelelement 260 can be calculated by graphics controller 210 based on aweighted sum of its red, green, and blue components (e.g.,Pixel_Luma=3R+B+4G, where R, B, and G represent the red, green, and bluecomponents of a pixel during the display of a given image). Graphicscontroller 210 can calculate the brightness for a number of pixelelements 260 for one or more images displayed by LCD 100 and keep trackof the number of pixel elements with a brightness that falls within twoor more brightness ranges. In other words, graphics controller 210 cancreate a histogram containing the number of pixel elements that have abrightness that falls within two or more brightness ranges. This datarepresenting the number of pixel elements having a brightness that fallswithin the two or more brightness ranges can then be passed to backlightcontroller 310 to interpret and/or adjust the sensed ambient light level320.

In yet another embodiment, backlight controller 310 can signal tographics controller 210, via graphics coordination signal 330, to adjustthe crystalline material to ensure a portion of the ambient light isable to pass through the display of LCD 100 so that it can be sensed bythe LEDs in LED) array 240 during the off states of one or more cyclesof PWM drive signal 295. Backlight controller 310 can, in a variant ofthis embodiment, signal to graphics controller 210, via graphicscoordination signal 330, to adjust only the crystalline materialcorresponding to particular regions or pixels of LCD 100 to ensure aportion of the ambient light is able to pass through the display.

FIG. 4 illustrates an exemplary block diagram of backlight module 110that includes both backlight controller 310 and LED array 240, accordingto embodiments of the present invention. As illustrated in FIG. 4,backlight controller 310 includes a bias generator 410, a pulse-widthmodulator 420, a brightness controller 430, and an LED array driver 440.

In operation, pulse-width modulator 420 is configured to provide apulse-width modulated (PWM) signal 450 to LED array driver 440. Eachperiod of PWM signal 450 has an on time and an off time. LED arraydriver 440 is configured to forward bias one or more of the LEDs in LEDarray 240 during the on time of PWM signal 450 and to reverse bias oneor more of the LEDs in LED array 240 during at least some of the offtimes of PWM signal 450.

During the portion of time that the one or more LEDs in LED array 240are forward biased, light is emitted and LCD 100 is illuminated. Duringthe portion of time that the one or more LEDs in LED array 240 arereverse biased, ambient light is sensed. In general, the one or moreLEDs in LED array 240 are transformed into photo diodes when reversebiased and produce a current, often referred to as a photocurrent, thatis roughly proportional to the amount of light striking their surfacesthrough the layers of LCD 100. Brightness controller 430 is able tomeasure or sense this current via ambient light level signal 320, asillustrated in FIG. 3.

In one embodiment, brightness controller 430 is configured to modulatethe duty-cycle of PWM signal 450 based on the ambient light level sensedby LED array 240. For example, in a room where the sensed ambient lightlevel 320 is fairly bright, brightness controller 430 can adjust theduty cycle of PWM signal 450 to provide a high brightness level.However, in a room where the sensed ambient light level 320 is fairlydim, brightness controller 430 can adjust the duty cycle of PWM signal450 to provide a low brightness level. The duty cycle is specificallyadjusted via pulse width control signal 470, as illustrated in FIG. 4.

In a further embodiment, additional control logic can be furtherutilized by brightness controller 430 to receive and use informationregarding the state of the crystalline material of LCD 100 to interpretand/or adjust the ambient light level sensed by the one or moredual-functioning LEDs. More specifically, the current orientation ortwist of the configurations of liquid crystal molecules corresponding toone or more pixel elements of LCD 100 at the time the ambient lightlevel is sensed by the one or more dual-functioning LEDs can be used tointerpret and/or adjust the sensed ambient light level 320.

For example, if the current orientation or twist of the configurationsof liquid crystal molecules is such that less light is allowed to passthrough the LCD display than what would otherwise be possible, then theambient light level sensed can be inflated and/or interpreted tocorrespond to an actual ambient light level having a brightness greaterthan what was actually sensed. This information regarding the state ofthe crystalline material of LCD 100 can be in the form of the voltageacross the capacitor corresponding to one or more pixel elements, or theamount of charge stored thereon, and can be received by brightnesscontroller 430 from the graphics controller of LCD 100 via graphicscoordination signal 330, as illustrated in FIG. 4.

In another embodiment, additional control logic can be further utilizedby brightness controller 430 to receive and use information regardingthe brightness of a number of pixel elements of LCD 100 to interpretand/or adjust the ambient light level sensed by the one or moredual-functioning LEDs. For example, the brightness, or luma, of a pixelelement can be calculated by graphics controller 210 based on a weightedsum of its red, green, and blue components (e.g., Pixel_Luma=3R+B+4G,where R, B, and G represent the red, green, and blue components of apixel during the display of a given image). Graphics controller 210 cancalculate the brightness for a number of pixel elements for one or moreimages displayed by LCD 100 and keep track of the number of pixelelements that have a brightness that falls within two or more brightnessranges. In other words, graphics controller 210 can create a histogramcontaining the number of pixel elements that have a brightness thatfalls within two or more brightness ranges. This data representing thenumber of pixel elements having a brightness that falls within the twoor more brightness ranges can then be passed via graphics coordinationsignal 330 to brightness controller 430 to interpret and/or adjust thesensed ambient light level 320.

In yet another embodiment, brightness controller 430 can signal to thegraphics controller, via graphics coordination signal 330, to adjust thecrystalline material to ensure a portion of the ambient light is able topass through the display of LCD 100 so that it can be sensed by the LEDsin LED) array 240 during the off states of one or more cycles of PWMsignal 450. Brightness controller 430 can, in a variant of thisembodiment, signal to the graphics controller, via graphics coordinationsignal 330, to adjust only the crystalline material corresponding toparticular regions or pixels of LCD 100 to ensure a portion of theambient light is able to pass through the display.

Bias generator 410 is configured to provide a forward bias voltage tothe LED array driver 440 during the on time of PWM signal 450 forforward biasing LED array 240 and a reverse bias voltage to LED arraydriver 440 during the off time of PWM signal 450 for reverse biasing theLED array. These two bias voltages are specifically provided to LEDarray driver 440 via V-BIAS signal 460, as illustrated in FIG. 4.

In one embodiment, brightness controller 430 is further configured tocontrol bias generator 410, via BALS enable signal 480, to provide thereverse bias voltage to LED array driver 440 only during the off time ofselect periods or cycles of PWM signal 450. For example, backlightcontroller 430 can be configured to control bias generator 410 toprovide the reverse bias voltage to LED array driver 440 only during theoff time of one out of every N periods of PWM signal 450, where N is aninteger number. In another example, backlight controller 430 can beconfigured to control bias generator 410 to provide the reverse biasvoltage to LED array driver 440 for M cycles in every N cycles of PWMsignal 450, where M and N are integer numbers and M is less than N.

It should be noted that PWM drive signal 295, provided by LED arraydriver 440, is substantially coordinated and identical to PWM signal450. However, the strength of PWM drive signal 295 is generally greaterin magnitude in order to forward bias and reverse bias LED array 240.

FIG. 5 illustrates an exemplary method 500 for adjusting the brightnessof LCD 100 based on ambient light conditions sensed by a backlightambient light sensor (BALS), according to embodiments of the presentinvention. In describing method 500, reference is made to the featuresdescribed above and illustrated in FIG. 4.

Method 500 of FIG. 5 starts at step 510 and transitions to step 520. Atstep 520, a determination is made at to whether PWM signal 450 iscurrently in an off state. If PWM signal 450 is not currently in an offstate, method 500 remains at step 520 until PWM signal 450 is determinedto be within an off state. If PWM signal 450 is currently in an offstate, method 500 transitions to step 530.

At step 530, a determination is made as to whether the current ambientlight conditions should be sensed. If not, method 500 transitions backto step 520 and waits for the next off state of PWM signal 450. If it isdetermined at step 530 that the current ambient light conditions shouldbe sensed, method 500 transitions to step 540.

At step 540, one or more of the LEDs in LED array 240 are reversebiased. While reverse biased, the one or more LEDs in LED array 240function as photo diodes and generate a current roughly proportional tothe amount of ambient light impacting their surfaces. Following step540, method 500 transitions to step 550.

At step 550, the magnitude of current produced by the one or more LEDsin LED array 240 is sensed and interpreted. This interpretation processcan, in one embodiment, include the use of information regarding thestate of the crystalline material of LCD 100 or information related to anumber of pixel elements of LCD 100 having a brightness that fell withintwo or more brightness ranges during the display of one or more images,as discussed above. After the sensory information is interpreted, method500 transitions to step 560.

At step 560, the brightness of one or more LEDs in LED array 240 isadjusted based on the sensory information. In one embodiment, theduty-cycle of PWM signal 450 is modulated based on the sensorinformation. For example, in a room where the sensed ambient light levelis fairly bright, the duty cycle of PWM signal 450 can be adjusted toprovide a high brightness level. However, in a room where the sensedambient light level is fairly dim, the duty cycle of PWM signal 450 canbe adjusted to provide a low brightness level.

4. Conclusion

It is to be appreciated that the Detailed Description section, and notthe Abstract section, is intended to be used to interpret the claims.The Abstract section may set forth one or more but not all exemplaryembodiments of the present invention as contemplated by the inventor(s),and thus, is not intended to limit the present invention and theappended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A backlight module comprising: a pulse-widthmodulator configured to provide a pulse-width modulated (PWM) signal; alight-emitting diode (LED) array driver configured to alternate, basedon the PWM signal, between forward biasing a LED array to backlight aliquid crystal display (LCD) and reverse biasing the LED array to sensean ambient light level; a bias generator configured to alternate, basedon the PWM signal, between providing a forward bias voltage to the LEDarray driver and providing a reverse bias voltage to the LED arraydriver; and a brightness controller configured to modulate a duty-cycleof the PWM signal based on the ambient light level sensed by the LEDarray, wherein, before using the ambient light level sensed by the LEDarray to modulate the duty-cycle of the PWM signal, the brightnesscontroller is configured to adjust the ambient light level sensed by theLED array based on a number of pixels of at least a portion of the LCDhaving a brightness that falls within one of a plurality of brightnessranges.
 2. The backlight module of claim 1, wherein the bias generatoris configured to provide the reverse bias voltage to the LED arraydriver only during select periods of the PWM signal.
 3. The backlightmodule of claim 1, wherein the bias generator is configured to providethe reverse bias voltage to the LED array driver only during one out ofevery N periods of the PWM signal, where N is an integer number.
 4. Thebacklight module of claim 1, wherein only a portion of the LED array isreverse biased by the LED array driver.
 5. The backlight module of claim1, wherein the brightness controller is further configured to adjust anamount of ambient light that is able to pass through the LCD.
 6. Thebacklight module of claim 1, wherein the brightness controller isfurther configured to modulate the duty-cycle of the PWM signal based ona current alignment of one or more liquid crystal molecules of the LCD.7. The backlight module of claim 1, wherein the brightness controller isfurther configured to coordinate with a graphics controller of the LCDto adjust an amount of ambient light that is able to pass through theLCD.
 8. A method for controlling a backlight module that includes alight-emitting diode (LED) array, the method comprising: providing apulse-width modulated (PWM) signal; alternating, based on the PWMsignal, between forward biasing the LED array to backlight a liquidcrystal display (LCD) and reverse biasing the LED array to sense anambient light level; modulating a duty-cycle of the PWM signal based onthe ambient light level sensed by the LED array, and before modulatingthe duty-cycle of the PWM signal based on the ambient light level sensedby the LED array, adjusting the ambient light level sensed by the LEDarray based on a number of pixels of at least a portion of the LCDhaving a brightness that falls within one of a plurality of brightnessranges.
 9. The method of claim 8, wherein the reverse biasing the LEDarray is only performed during select periods of the PWM.
 10. The methodof claim 8, wherein the LED array is only reverse biased during one outof every N periods of the PWM signal, where N is an integer number. 11.The method of claim 8, wherein only a portion of the LED array isreverse biased.
 12. The method of claim 8, further comprising: adjustingan amount of ambient light that is able to pass through the LCD.
 13. Themethod of claim 8, wherein the modulating the duty-cycle of the PWMsignal is further performed based on a current alignment of one or moreliquid crystal molecules of the LCD.
 14. A backlight module comprising:a pulse-width modulator configured to provide a pulse-width modulated(PWM) signal; a light-emitting diode (LED) driver configured toalternate, based on the PWM signal, between forward biasing a LED tobacklight a liquid crystal display (LCD) and reverse biasing the LED tosense an ambient light level; a bias generator configured to alternate,based on the PWM signal, between providing a forward bias voltage to theLED driver and providing a reverse bias voltage to the LED driver; and abrightness controller configured to modulate a duty-cycle of the PWMsignal based on the ambient light level sensed by the LED, wherein,before using the ambient light level sensed by the LED to modulate theduty-cycle of the PWM signal, the brightness controller is configured toadjust the ambient light level sensed by the LED based on a number ofpixels of at least a portion of the LCD having a brightness that fallswithin one of a plurality of brightness ranges.
 15. The backlight moduleof claim 14, wherein the bias generator is configured to provide thereverse bias voltage to the LED driver only during select periods of thePWM signal.
 16. The backlight module of claim 14, wherein the biasgenerator is configured to provide the reverse bias voltage to the LEDdriver only during one out of every N periods of the PWM signal, where Nis an integer number.
 17. The backlight module of claim 14, wherein thebrightness controller is further configured to adjust an amount ofambient light that is able to pass through the LCD when the reverse biasvoltage is provided to the LED driver.
 18. The backlight module of claim14, wherein the brightness controller is further configured to modulatethe duty-cycle of the PWM signal based on a current alignment of one ormore liquid crystal molecules of the LCD.
 19. The backlight module ofclaim 14, wherein the brightness controller is further configured tocoordinate with a graphics controller of the LCD to adjust an amount ofambient light that is able to pass through the LCD when the reverse biasvoltage is provided to the LED driver.
 20. The backlight module of claim14, wherein the brightness controller is further configured tocoordinate with a graphics controller of the LCD to adjust an amount ofambient light that is able to pass through only a portion of the LCDwhen the reverse bias voltage is provided to the LED driver.